A bioabsorbable coating for a surgical article comprises a copolymer manufactured from the monomer caprolactone and at least one other copolymerizable monomer. The surgical article can be a bioabsorbable suture or a ligature. A surgical suture or ligature coated with the bioabsorbable copolymer of this invention has improved knot repositioning properties.
The bioabsorbable coating of this invention has advantages over prior art coatings used with surgical stutures or ligatures. Specifically, sutures coated with the copolymer coating of this invention are less stiff than sutures using the coatings described in the prior art; see examples 6 and 10 in U.S. Pat. Nos. 3,867,190 and 3,736,646 which are incorporated herein by reference. Also, the processes for coating a bioabsorbable surgical article are not clearly described in the prior art. That is, the process of this invention uses a copolymer manufactured from at least about 50 percent by weight of the monomer caprolactone and the remainder glycolide. Copolymers of these proportions are soluble in acetone, as contrasted with, for example, the copolymers of lactide and glycolide discussed in U.S. Pat. No. 4,201,216, which is incorporated herein by reference.
The use of a copolymer of caprolactone and glycolide as a suture is known in the prior art, for example, as disclosed in U.S. Pat. Nos. 4,700,704 (e.g. claim 1) and 4,605,730 (examples I to XI), and in example 5 of U.S. Pat. Nos. 4,300,565 and 4,243,775. All of these patents are incorporated herein by reference.
The use of a copolymer of at least 90% by weight caprolactone and another biodegradable monomer, e.g. glycolide, as a coating is disclosed in U.S. Pat. No. 4,624,256. See also U.S. Pat. Nos. 4,190,720 (column 1) and 3,942,532 (example II), which are disclosed in the '256 patent. These two latter patents disclose a copolymer ('720) or homopolymer ('532) of .epsilon.-caprolactone. In the '720 patent, the copolymer is disclosed as a film; in the '532 patent the homopolymer is dislcosed as a suture coating. It is not seen in either of the latter two patents where the respective polymers are disclosed as bioabsorbable. All of these patents are incorporated herein by reference.
The bioabsorbable coating of this invention has superior and unexpected results over the known commercially available surgical suture or ligature coatings. For example, the coating of this invention does not present a hazy appearance on a suture. The coating can be dissolved in acetone which seems to be less deleterious than other known solvents, for example, methylene chloride. Further, suture characteristics such as knot-snug-in or repositioning, and tissue drag appear to be equal to, if not better than suture coatings disclosed in the prior art.
A bioabsorbable coating for a surgical article comprising a block copolymer has been invented. The block copolymer has one or more blocks manufactured from the monomer caprolactone.
The term block copolymer described in this invention means a copolymer with a non-random distribution of comonomer units along the chain. A convenient shorthand notation to describe different block architectures utilizes alphabetic symbols for the individual block segments. The number and types of comonomer units within a block segment can be specified. For example, AB represents a diblock copolymer, ABA or BAB represents a triblock copolymer. More complex architectures such as tetrablocks or pentablocks, etc., can also be described using this notation, e.g., ABABA. A multiblock copolymer can be represented as --AB--.sub.n. If more than two types of blocks are present, additional alphabetic symbols can be defined.
Block copolymers are formed in this ivnention by the sequential addition of comonomers or mixtures of comonomers to a reactor. It is believed that with this type of preparation method, there can be a distribution of block size and block composition and that the chain architecture can be compromised by ester interchange reactions.
The term random or randomly in this invention means the result of a copolymerization reaction in which all of the monomers are charged into a reactor simultaneously. It is to be understood that variations in reaction conditions can lead to some differences in the actual degree of randomness with respect to the distribution of comonomer units in a copolymer chain.
In one embodiment, the caprolactone is .epsilon.-caprolactone. In another embodiment the copolymer is a diblock copolymer.
In a preferred embodiment, the copolymer has one or more A blocks solely manufactured from the monomer caprolactone, and one or more B blocks manufactured from one or more monomers selected from the group consisting of lactides, carbonates, lactones and oxalates, with the proviso that in the latter one or more B blocks, caprolactone can only be used with another monomer. In a further embodiment, the inherent viscosity of the block copolymer is about 0.1 to 1.0 dl/g (0.5 g/dl in CHCl.sub.3 , 30.degree. C.), the melting point of the block copolymer is less than 70.degree. C., and the block copolymer is soluble in acetone or methylene chloride.
In a specific embodiment, the coating comprises a block copolymer consisting of one or more A blocks of formula (I): ##STR1## and the remaining one or more B blocks comprising one or more of the formulas (II) to (VI), either alone or in combination with formula (I): ##STR2## the total amount of formula (I) in the copolymer being more than 50 to about 80 percent by weight of said copolymer.
In one embodiment, the remaining one or more B blocks consist of formulas (I) and (II). In another embodiment the remaining one or more B blocks consist of formulas (II) and (III).
In a specific embodiment, the formula (II) is: ##STR3##
The surgical article coated with the above-described polymers can be bioabsorbable. In one embodiment, the bioabsorbable surgical article is a suture or ligature. In a specific embodiment, the suture or ligature is manufactured from a polymer prepared from one or more monomers selected from the group consisting of lactides, carbonates and lactones. If the polymer in the suture or ligature and the copolymer in the coating are prepared from the same monomers, it is to be understood that the copolymer in the coating has a melting point less than about 70.degree. C. and is soluble in acetone or methylene chloride. It is to be further understood that this description applies by implication to the description of the invention in the claims.
In a more specific embodiment, the suture or ligature is manufactured from a homopolymer prepared from the monomer glycolide. In another specific embodiment, the suture or ligature is manufactured from a polymer prepared from at least the monomer lactide. In yet another more specific embodiment, the suture or ligature is manufactured from a copolymer prepared from the monomers glycolide and 1,3-dioxan-2-one. In a further specific embodiment, the suture or ligature is manufactured from a copolymer prepared from the monomers glycolide and lactide.
The suture or ligature can be in multifilamentary form. In a specific embodiment, the coating comprises about 1/10 to 5% by weight of the coated multifilamentary suture or ligature. In a more specific embodiment, the coating comprises about 1/4 to 3% by weight of the coated multifilamentary suture or ligature. In the more specific embodiment, the coating can comprise up to about 2 1/2 percent by weight of the coated multifilamentary suture or ligature.
A coating process for a bioabsorbable surgical article comprises dissolving in acetone a block copolymer having one or more A blocks manufactured solely from the monomer caprolactone and one or more B blocks manufactured from the monomers caprolactone and glycolide, where the glycolide in the one or more B blocks comprises up to 50 percent by weight of the copolymer and up to about 65 percent by weight of said B blocks; contacting the surgical article with the dissolved copolymer; maintaining the contact between the surgical article and the dissolved copolymer until the copolymer on the article comprises from about 1/10 to 5% by weight of the coated surgical article; removing the coated surgical article from the dissolved copolymer; and drying the copolymer coating on the surgical article.
In one embodiment, the caprolactone is .epsilon.-caprolactone.